Barrier coatings which prevent, reduce, or inhibit the permeation of a selected substrate with a gas, vapor, chemical and/or aroma have been widely described, and such coatings are used in a variety of industries, e.g., the packaging industry, automobile industry, paint industry, and tire industry. For example, butyl rubber in automobile tires has been coated with formulations which includes a polymer and a platelet filler, in order to reduce the air permeability of the tire. See, e.g., U.S. Pat. Nos. 4,911,218 and 5,049,609. Tires with integral innerliners are disclosed in U.S. Pat. No. 5,178,702, wherein the tire includes rubber laminate in which at least two layers are barrier layers having 100 parts by weight rubber, 100 parts by weight acrylonitrile/diene polymer and about 25-150 parts by weight of platelet filler of unspecified width and thickness. These compositions are stated to reduce the costs of the innerliners while maintaining flexibility and barrier performance.
The use of exfoliated silicates to produce nanocomposite barrier coatings has been achieved by several methods. The most widely used has been by combining a dissolved polymer with exfoliated filler. Water soluble polymers such as polyvinyl alcohol (PVOH) have been combined with water exfoliated filler such as vermiculite. See, Japan Patent 11-246729, Sep. 14, 1999, “Gas-Barrier Poly(vinyl alcohol)/poly (acrylic acid) Compositions and their Laminates and Shaped Articles.” Sumitomo Chemical Co., Ltd. Polycarbonate polymers have been dissolved in toluene and combined with organically functionalized filler to form good barrier coatings. W. J. Ward et al., “Gas Barrier Improvement Using Vermiculite and Mica in Polymer Films”, Journal of Membrane Science, 55:173-180 (1991)]. Other polymers have also been made into improved barrier coatings by dissolving them in a solvent, and using an organically functionalized filler to improve the barrier properties. See, e.g., Yano, K. et al., “Synthesis and Properties of Polyimide-Filler Hybrid Composites”, Journal of Polymer Science A: Polymer Chemistry, 35, 2289 (1997).
There are several examples of using an aqueous dispersion of exfoliated filler with an aqueous dispersion of polymer to form a nanocomposite. Most of that work used elastomeric polymers in suspension. See, for example, Wu, Y-P et al., “Structure of Carboxylated Acrylonitrile-Butadiene Rubber (CNBR)-Filler Nanocomposites by Co-coagulating Rubber Latex and Filler Aqueous Suspension”, Journal of Applied Polymer Science, 82, 2842-2848 (2001); Wu, Y-P et al., “Structure and Properties of Nitrile Rubber (NBR)-Filler Nanocomposites by Co-coagulating NBR Latex and Filler Aqueous Suspension”, Journal of Applied Polymer Science, 89, 3855-3858 (2003); Varghese and Karger-Kocsis, “Natural Rubber-Based Nanocomposites by Latex Compounding with Layered Silicates”, Polymer (in press) (2003); Feeney et al., U.S. Pat. No. 6,087,016, “Barrier Coating of an Elastomer and a Dispersed Layered Filler in a Liquid Carrier”, Jul. 11, 2000; Feeney et al., U.S. Pat. No. 6,232,389, “Barrier Coating of an Elastomer and a Dispersed Layered Filler in a Liquid Carrier and Coated Articles”, May 15, 2001; Goldberg et al., “Nanocomposite Barrier Coatings for Elastomeric Applications”, Materials Research Society, Symposium T: Polymer nanocomposites, paper T4.7, (April 2002); and Goldberg et al, “Elastomeric Barrier Coatings for Sporting Goods”, ACS Rubber Section, Apr. 29, 2002, paper 17, published in Rubber World, vol. 226, No. 5, p. 15 (August 2002).
Other references of interest include U.S. Pat. No. 4,472,538 to Kamigaito et al.; U.S. Pat. No. 4,889,885 to Usuki et al.; U.S. Pat. No. 6,087,016 to Feeney et al.; and U.S. Pat. No. 6,232,289 to Feeney et al.
Despite the contributions in the art, there exists a need for an aqueous coating composition that exhibits enhanced barrier properties, which may be applied to other polymer films. Such a coating would be particularly useful in packaging applications where the package contents spoil or degrade upon contact with air. There further exists a need for a coating material which can be provided in a processable and economical form, whereby the coating can be produced at a high solids content without gelling.